The construction and the operation of a conventional bead fluidizing type body supporting device will first be explained with reference to FIG. 1. A bed 1 comprises a box-like vessel 3 of a size sufficient to enable a patient 2 to lie thereon, ceramic beads 4, for example, minute glass or ceramic particles having specific gravity of 2-3 and particle size of about 50-150 u, a gas permeable filter sheet 5 covering the upper surface of the vessel 3 and secured to the peripheral edge thereof with a mesh finer than the particle size of the beads 4, a plenum chamber 6 disposed on the bottom side of the vessel 3, a porous air diffusion plate 7 disposed at the boundary between the plenum chamber 6 and the vessel 3, an air blower 9 accommodated within a machine chamber 8, a conduit 10 for connecting the air blower 9 and the plenum chamber 6 to supply compressed air, and a heat dissipator 11 disposed midway in the conduit 10. The ceramic beads 4 may be coated with a resin.
In such a construction, the beads 4 are stationary when the air blower 9 is not operated to give the patient 2 lying on the bed a feeling like that of lying on sand. When the air blower 9 is operated to blow compressed air into the vessel 3 by way of the plenum chamber 6 and the air diffusion plate 7, as shown by the arrow A, the compressed air permeates throughout the inside of the vessel 3. The beads 4, sealed within the vessel 3 by the filter sheet 5, are fluidized by the streams of the compressed air to establish a floating state.
In the floating state, the apparent specific gravity of the beads 4 is reduced to about 1.1-1.2 to sustain the patient lying thereon in a substantially floating state wherein the contact pressure between the patient 2 and the bed 1 is greatly reduced and the patient feels as if he is floating in the air. The compressed air continuously passes through the vessel 3, permeates the sheet 5, and is diffused into the surrounding room. The air exhausted from the air blower 9 is heated about 10-20 degrees in the compression stroke. If air at such a high temperature is directly blown against the patient 2 troubles in the therapy may arise. Accordingly, the heat dissipator 11 must be provided at the midway point of the conduit 10.
Such a body supporting device, however, can provide therapeutic effects in treatment of a patient suffering from burns and suppress contact pressure to lesions. Decreasing the contact pressure between a patient undergoing long time therapy and a bed can also prevent bedsores.
In the conventional body sustaining device as described above, if a patient changes his position from that of lying to that of sitting on the bed, his body weight is localized and his hips sink to result in an unstable position. Further, if the depth of the bed vessel 3 is small, the hip may come in direct contact with the hard air diffusion plate 7 and suffer from strong contact pressure. If the patient sits for a long period of time, the increased contact pressure is undesirable from the perspective of preventing bedsores.
It is not practicable to prevent such excess sinking of the body by increasing the volume and pressure of the air blown into the vessel from the air blower 9 to increase the floating effect of the fluidized beads. This is because the air stream blown out from the sheet 5 would be increased excessively and the mechanical noise would become undesirable.